Whether the bottle-making process is an ISBM process where the injected preliminary products are typically referred to as “preforms” or an IBM process where the injected products are typically called “parisons”, the hot melt begins to cool the instant it enters an injection cavity because such cavities are relatively much colder than the distribution manifolds and injection nozzles through which the melt travels on its way to the injection cavities. (For the sake of simplicity, the term “preform” will hereinafter be used to refer collectively to both preforms and parisons, with the understanding that either or both an ISBM and an IBM process are contemplated.) Thus, if melt enters some of the cavities of a set of multiple cavities at a slightly different time than others and/or at a different rate, the melt in some cavities will cool at different rates than others, and some will not have as much time to cool down as others before the preforms are pulled out of the injection mold for the next stage in the process. This can have very significant consequences in the quality and consistency of the finished bottle products.
These variations in melt delivery time and fill rate are due in part to the nature and construction of conventional manifold systems. In conventional manifolds hot melt typically flows along a main runner into multiple branch passages that lead to the injection cavities. Passages that are more remote than others from the main inlet to the runner do not receive their melt at the same time as others, and their rates of fill are slower. While it is known in the art to attempt to deal with this imbalance problem by making the passages leading to the cavities different diameters, depending upon their distance from the main inlet, this practice significantly complicates manufacture of the tooling and can lead to time-consuming and costly trial-and-error efforts to achieve just the right set of dimensions for the tooling.
The present invention addresses these problems by providing adjustable restrictor devices in operable association with at least some of the branch passages in a distribution manifold so that the time of delivery of the hot melt into all of the injection cavities in the set can be synchronized and the rate of fill can be rendered essentially uniform across all of cavities of the set. In a preferred embodiment, all of the branch passages can be of the same diameter, and all of the nozzle tips and nozzle passages can likewise be of uniform diameter from one nozzle to another so as to simplify manufacture. Furthermore, in a preferred embodiment the restrictors are in the nature of pins that are aligned axially with the branch passages at their intersections with the main runner and which can be axially adjusted to move into and out of the branch passage to achieve the desired degree of constriction. Outermost branches that are most remote from the inlet to the main runner may be devoid of such restrictor pins, while those branches closer to the inlet may be provided with pins to the extent necessary. Preferably, adjustment is carried out by threading the pins into and out of the body of the manifold to the extent desired.